Multi-cylinder internal combustion engine and method for operating a multi-cylinder internal combustion engine

ABSTRACT

A method for partial cylinder cutoff is provided. The method comprises operating a multi-cylinder internal combustion engine with applied ignition, in which an odd number n of cylinders is arranged in line, and during partial-load operation when engine load is below threshold, enabling a partial cutoff of the cylinders, the partial cutoff comprising operating each cylinder only intermittently such that each cylinder is fired and cut off in turn at an interval of (2*720° CA)/n.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/224,228, entitled “MULTI-CYLINDER INTERNAL COMBUSTION ENGINEAND METHOD FOR OPERATING A MULTI-CYLINDER INTERNAL COMBUSTION ENGINE,”filed on Sep. 1, 2011, which claims priority to German PatentApplication No. 102010037362.1, filed on Sep. 7, 2010, the entirecontents of each of which are hereby incorporated by reference for allpurposes.

FIELD

The disclosure relates to a multi-cylinder internal combustion enginewith applied ignition.

BACKGROUND AND SUMMARY

Spark-ignition engines operate with a homogeneous fuel-air mixturewhich, in the absence of direct injection, is prepared through externalmixture formation by introducing fuel into the intake air in the intaketract. The required power output is adjusted by varying the combustionchamber charge so that, unlike in the diesel engine, operation of thespark-ignition engine is based on a quantitative control.

The load is generally controlled by means of a throttle valve providedin the intake tract. By adjusting the throttle valve the pressure of theintake air downstream of the throttle valve can be reduced to a greateror lesser degree. The further the throttle valve is closed, the greaterthe pressure loss of the intake air over the throttle valve and thelower the pressure of the intake air downstream of the throttle valveand upstream of the inlet to the cylinder. Given a constant combustionchamber volume it is possible in this way to adjust the air mass, thatis to say the quantity, by way of the intake air pressure. However, inthe partial load range, since small loads require a high degree ofthrottling and pressure reduction in the intake tract, charge cyclelosses increase as the load diminishes and the throttling increases. Asa result, engine efficiency and thus fuel economy are compromised.

Various strategies have been developed for dethrottling an internalcombustion engine with applied ignition, in order to reduce the lossesdescribed. Since in partial load operation the spark-ignition engine hasa poor efficiency due to the throttle control, whereas the diesel enginehas a greater efficiency, attempts have been made to combine the twomethods of operation with one another, in order to exploit theadvantages of the diesel engine method for the benefit of thespark-ignition engine method. Here the development work has concentratedprimarily on the essential features of the two methods. The conventionalspark-ignition method is characterized by a mixture compression, ahomogeneous mixture, an applied ignition, and the quantitative control,whereas the conventional diesel engine method is characterized by an aircompression, an inhomogeneous mixture, a compression ignition and thequalitative control.

One approach to dethrottling, for example, is to operate thespark-ignition engine with direct injection. Direct fuel injection is asuitable means for achieving a stratified combustion chamber charge.Within certain limits, the direct injection of fuel into the combustionchamber thereby allows a qualitative control in the spark-ignitionengine. The mixture formation ensues through the direct injection offuel into the cylinders or rather the air present in the cylinders andnot through external mixture formation, in which the fuel is introducedinto the intake air in the intake tract.

Another possible way of optimizing the combustion process of aspark-ignition engine lies in the use of a variable valve gear. Incontrast to conventional valve gears, in which both the valve lift andalso the timings, that is to say the opening and closing times of theintake and exhaust valves, are predetermined as invariable quantities bythe non-adjustable and hence inflexible mechanism of the valve gear,these parameters influencing the combustion process and thereby the fuelconsumption can be varied to a greater or lesser degree by means ofvariable valve gears. A load control with no throttle and thereby nolosses is possible simply by being able to vary the closing time of theintake valve and the intake valve lift.

The concepts described above have the disadvantage that they are notsuitable for retrofitting to engines already on the market, since theyrequire substantial modifications to the basic engine and/or the valvegear, and additional complex components.

One approach to the dethrottling of spark-ignition engines already onthe market is afforded by the cylinder cutoff. This serves to improve,that is to say to increase the efficiency in the partial-load rangesince the cutoff of one cylinder of a multi-cylinder internal combustionengine increases the load of the cylinders in operation, so that thethrottle valve may be opened further in order to introduce a larger airmass into these cylinders, so that overall a dethrottling of theinternal combustion engine is achieved. Owing to the larger air massdelivered, the cylinders still being operated during the partial cutoffhave an improved mixture formation and tolerate higher exhaust gasrecirculation rates. Further advantages in terms of efficiency accrue inthat owing to the absence of combustion a cylinder which has been cutoff does not generate any heat losses through the wall due thetransmission of heat from the combustion gases to the combustion chamberwalls.

Besides the aforementioned advantages, partial cutoff, particularly inmulti-cylinder internal combustion engines having an odd number n ofcylinders, also have disadvantages, which are often an obstacle to usein series production. Conventionally, in an inline three-cylinderengine, for example, one cylinder of the engine is embodied as a cutoffcylinder. In normal operation, that is to say when all three cylindersare in operation and the partial cutoff is deactivated, the cylindersare fired in the firing order 1-2-3 at an interval of 240° CA. In thecontext of a partial cutoff, the cutoff cylinder is deactivated and onlythe two remaining cylinders continue to operate, so that an irregularfiring pattern ensues, in which the firing interval alternates between240° CA and 480° CA, which results in several detrimental effects.

The engine structure excited to structure-borne sound oscillations bythe impulses and alternating forces emits the structure-borne sound viaits engine surfaces as airborne sound and in this way generates theactual engine noise. The irregular firing pattern leads to anunharmonious engine noise, which is perceived as unpleasant. This isdisadvantageous, since the noise generated by the internal combustionengine has a considerable influence on customers' purchasing behavior.Further, excitation of the crankshaft in the natural frequency range canresult in high rotational oscillation amplitudes, which can even lead tofatigue fracture.

The problems discussed taking a three-cylinder internal combustionengine as an example similarly exist in any multi-cylinder internalcombustion engine, in which an odd number n of cylinders is arranged inline, for example also in the case of a five-cylinder internalcombustion engine, in which five cylinders are arranged in line.

The inventors herein have recognized the above issues and provide asolution to at least partially address them. Thus, a method foroperating a multi-cylinder internal combustion engine with appliedignition having an odd number n of cylinders arranged in line isprovided. The method comprises operating a multi-cylinder internalcombustion engine with applied ignition, in which an odd number n ofcylinders is arranged in line, and, during partial-load operation whenengine load is below threshold, enabling a partial cutoff of thecylinders, the partial cutoff comprising operating each cylinder onlyintermittently such that each cylinder is fired and cut off in turn atan interval of (2*720° CA)/n.

In the method according to the present disclosure, in normal operation,when all n cylinders are being operated and the partial cutoff isdeactivated, the n cylinders are fired at a firing interval ofapproximately 720° CA/n. During the partial cutoff, on the other hand,each cylinder is operated intermittently and in such a way that eachcylinder is fired and cut off in turn, so that in partial load operationthe cylinders are fired in a modified firing order and at a firinginterval of approximately (2*720° CA)/(n). The firing interval thereforedoubles with a partial cutoff of the cylinders. The partial cutoffaccording to the disclosure leads to a uniform firing interval, that isto say to a regular firing pattern, and thereby to a harmonious enginenoise.

In a multi-cylinder, in-line engine having an odd number of cylindersand applied ignition, the method for partial cutoff according to thepresent disclosure makes it possible to reduce the charge cycle losseswhich are bound to occur due to the quantitative control by means of athrottle valve, whilst avoiding an irregular firing pattern, in whichthe firing interval varies and which has a detrimental effect on thenoise emissions. Thus, dethrottling of the engine can be achievedwithout having to accept disadvantages in terms of the noise emissions.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of an engine including a cylinder andan ignition system.

FIG. 2 shows a flow diagram illustrating an example method for operatingan engine in partial cutoff mode.

FIG. 3 shows an example diagram of the ignition points of the threecylinders of a three-cylinder in-line engine with applied ignition innormal, full cylinder operation.

FIG. 4 shows an example diagram of the ignition points of the threecylinders of the three-cylinder in-line engine with applied ignition inpartial cutoff.

FIG. 5 shows an example diagram of the ignition points of the threecylinders of a three-cylinder in-line engine with applied ignition in atransition from the normal, full cylinder operation to the partialcutoff.

FIG. 6 shows an example diagram of the ignition points of the threecylinders of a three-cylinder in-line engine with applied ignition in atransition from the partial cutoff operation to the normal, fullcylinder operation.

DETAILED DESCRIPTION

In order to dethrottle the engine to improve fuel economy, a partialcylinder cutoff may be activated in which each cylinder is cut off inturn. FIG. 1 shows an example engine that can be operated in the partialcutoff mode according the method of FIG. 2. FIGS. 3-6 depict ignitiontiming diagrams during the execution of the method of FIG. 2.

Referring now to FIG. 1, a schematic diagram showing one cylinder ofmulti-cylinder engine 10, which may be included in a propulsion systemof an automobile, is illustrated. Engine 10 may be controlled at leastpartially by a control system including controller 12 and by input froma vehicle operator 132 via an input device 130. In this example, inputdevice 130 includes an accelerator pedal and a pedal position sensor 134for generating a proportional pedal position signal PP. Combustionchamber (i.e., cylinder) 30 of engine 10 may include combustion chamberwalls 32 with piston 36 positioned therein. Piston 36 may be coupled tocrankshaft 40 so that reciprocating motion of the piston is translatedinto rotational motion of the crankshaft. Crankshaft 40 may be coupledto at least one drive wheel of a vehicle via an intermediatetransmission system. Further, a starter motor may be coupled tocrankshaft 40 via a flywheel to enable a starting operation of engine10.

Combustion chamber 30 may receive intake air from intake manifold 44 viaintake passage 42 and may exhaust combustion gases via exhaust passage48. Intake manifold 44 and exhaust passage 48 can selectivelycommunicate with combustion chamber 30 via respective intake valve 52and exhaust valve 54. In some embodiments, combustion chamber 30 mayinclude two or more intake valves and/or two or more exhaust valves.

In this example, intake valve 52 and exhaust valves 54 may be controlledby cam actuation via respective cam actuation systems 51 and 53. Camactuation systems 51 and 53 may each include one or more cams and mayutilize one or more of cam profile switching (CPS), variable cam timing(VCT), variable valve timing (VVT), and/or variable valve lift (VVL)systems that may be operated by controller 12 to vary valve operation.The position of intake valve 52 and exhaust valve 54 may be determinedby position sensors 55 and 57, respectively. In alternative embodiments,intake valve 52 and/or exhaust valve 54 may be controlled by electricvalve actuation. For example, cylinder 30 may alternatively include anintake valve controlled via electric valve actuation and an exhaustvalve controlled via cam actuation including CPS and/or VCT systems.

In some embodiments, each cylinder of engine 10 may be configured withone or more fuel injectors for providing fuel thereto. As a non-limitingexample, cylinder 30 is shown including one fuel injector 66, which issupplied fuel from fuel system 172. Fuel injector 66 is shown coupleddirectly to cylinder 30 for injecting fuel directly therein inproportion to the pulse width of signal FPW received from controller 12via electronic driver 68. In this manner, fuel injector 66 provides whatis known as direct injection (hereafter also referred to as “DI”) offuel into combustion cylinder 30.

It will be appreciated that in an alternate embodiment, injector 66 maybe a port injector providing fuel into the intake port upstream ofcylinder 30. It will also be appreciated that cylinder 30 may receivefuel from a plurality of injectors, such as a plurality of portinjectors, a plurality of direct injectors, or a combination thereof.

Continuing with FIG. 1, intake passage 42 may include a throttle 62having a throttle plate 64. In this particular example, the position ofthrottle plate 64 may be varied by controller 12 via a signal providedto an electric motor or actuator included with throttle 62, aconfiguration that is commonly referred to as electronic throttlecontrol (ETC). In this manner, throttle 62 may be operated to vary theintake air provided to combustion chamber 30 among other enginecylinders. The position of throttle plate 64 may be provided tocontroller 12 by throttle position signal TP. Intake passage 42 mayinclude a mass air flow sensor 120 and a manifold air pressure sensor122 for providing respective signals MAF and MAP to controller 12.

Ignition system 88 can provide an ignition spark to combustion chamber30 via spark plug 92 in response to spark advance signal SA fromcontroller 12, under select operating modes. Though spark ignitioncomponents are shown, in some embodiments, combustion chamber 30 or oneor more other combustion chambers of engine 10 may be operated in acompression ignition mode, with or without an ignition spark.

An upstream exhaust gas sensor 126 is shown coupled to exhaust passage48 upstream of emission control device 70. Upstream sensor 126 may beany suitable sensor for providing an indication of exhaust gas air-fuelratio such as a linear wideband oxygen sensor or UEGO (universal orwide-range exhaust gas oxygen), a two-state narrowband oxygen sensor orEGO, a HEGO (heated EGO), a NO_(x), HC, or CO sensor.

Emission control device 70 is shown arranged along exhaust passage 48downstream of exhaust gas sensor 126. Device 70 may be a three waycatalyst (TWC), configured to reduce NOx and oxidize CO and unburnthydrocarbons. In some embodiments, device 70 may be a NO_(x) trap,various other emission control devices, or combinations thereof.

A second, downstream exhaust gas sensor 128 is shown coupled to exhaustpassage 48 downstream of emissions control device 70. Downstream sensor128 may be any suitable sensor for providing an indication of exhaustgas air-fuel ratio such as a UEGO, EGO, HEGO, etc.

Further, in the disclosed embodiments, an exhaust gas recirculation(EGR) system may route a desired portion of exhaust gas from exhaustpassage 48 to intake passage 42 via EGR passage 140. The amount of EGRprovided to intake passage 42 may be varied by controller 12 via EGRvalve 142. Further, an EGR sensor 144 may be arranged within the EGRpassage and may provide an indication of one or more of pressure,temperature, and concentration of the exhaust gas. Under someconditions, the EGR system may be used to regulate the temperature ofthe air and fuel mixture within the combustion chamber.

Controller 12 is shown in FIG. 1 as a microcomputer, includingmicroprocessor unit 102, input/output ports 104, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 106 in this particular example, random access memory 108,keep alive memory 110, and a data bus. Controller 12 may receive varioussignals from sensors coupled to engine 10, in addition to those signalspreviously discussed, including measurement of inducted mass air flow(MAF) from mass air flow sensor 120; engine coolant temperature (ECT)from temperature sensor 112 coupled to cooling sleeve 114; a profileignition pickup signal (PIP) from Hall effect sensor 118 (or other type)coupled to crankshaft 40; throttle position (TP) from a throttleposition sensor; and absolute manifold pressure signal, MAP, from sensor122. Engine speed signal, RPM, may be generated by controller 12 fromsignal PIP.

Storage medium read-only memory 106 can be programmed with computerreadable data representing non-transitory instructions executable byprocessor 102 for performing the methods described below as well asother variants that are anticipated but not specifically listed.

As described above, FIG. 1 shows only one cylinder of a multi-cylinderengine, and each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector, spark plug, etc.

FIG. 2 is a flow diagram illustrating a method 200 for operating anengine in a partial cutoff mode according to an embodiment of thepresent disclosure. Method 200 comprises, at 202, determining if engineload and/or speed are below a threshold. Partial cutoff of the cylindersmay be activated when engine load is a below a threshold. The thresholdmay be any suitable engine load below which throttle position, fuelinjection amounts, etc. may lead to reduced fuel economy, such as 20%load, 30% load, etc. Further, the load threshold may vary as a functionof engine speed. For example, at higher engine speeds, the loadthreshold may be lower than at lower engine speeds. This means thatthere is not only an actual load, below which one cylinder is cut off asa function of the engine speed, but rather an engine speed-dependentapproach defining a partial load range within a speed-load map, in whicha partial cutoff is undertaken.

If it is determined at 202 that engine load and/or speed are not belowthe threshold, method 200 proceeds to 204 to fire all cylinders. In thecontext of the present disclosure, firing a cylinder means that acombustible or ignitable fuel-air mixture is provided in the cylinder,the ignition is initiated, that is to say an ignition spark isintroduced, and the fuel-air mixture ignites and is burned. In thisrespect there is a difference between the ignition and the initiation ofthe applied ignition, that is to say the activation of the appliedignition. Firing all the cylinders comprises firing one cylinder every720°/n CA at 206. For example, in a three-cylinder engine (n=3) when allthree cylinders are in operation, the cylinders may be fired in thefiring order 1-2-3 at an interval of 240° CA. In other embodiments, forexample in a five cylinder engine (n=5), the five cylinders may be firedin sequence in the ignition order 1-2-4-5-3 at an interval of 144° CA.For the purposes of this disclosure, the numbering of the cylinders isgoverned by DIN 73021. In the case of in-line engines the cylinders arenumbered continuously in series, starting on the side situated oppositethe clutch.

In order to fire the cylinders, fuel injection to all cylinders isenabled at 208. To ignite the fuel delivered to the cylinders, airflowthrough each cylinder is maintained at 210 and spark is enabled for eachcylinder at 212. Additionally, the throttle position and the amount offuel delivered are set to maintain the operator requested torque at 214.

If it is determined at 202 that engine load and/or speed are below thethreshold, method 200 proceeds to 216 to enable partial cylinder cutoffoperation. In partial-load operation one cylinder is cut off, so thatthe load demand on the remaining cylinders is increased. This requiresan opening of the throttle valve in order to introduce a larger mass ofair into these cylinders and leads to a dethrottling of the internalcombustion engine. Enabling partial cutoff operation comprises, at 218,sequentially deactivating each cylinder, and firing one active cylinderevery (2*720)/n CA°. No specific cylinder of the engine is embodied asthe cutoff cylinder and deactivated in the context of a partial cutoff,but rather each cylinder is fired and deactivated. That is to say, eachcylinder is cut off in turn during a partial cutoff in partial-loadoperation, with only one cylinder at a time being cut off and theremaining cylinders being in operation. A suitable firing orderadvantageously ensures a regular firing pattern.

For example, in a three-cylinder engine, during partial cutoff, wheneach cylinder is fired for one working cycle and is cut off for oneworking cycle, the firing order starting from operation of the firstcylinder in the working cycle may be 1-3-2 with a uniform firinginterval of 480° CA. In another embodiment, in a five cylinder engine,during the partial cutoff each cylinder is operated intermittently insuch a way that each cylinder is fired and cut off in turn, so that inpartial-load operation the cylinders may be fired in a modified firingorder 1-4-3-2-5 at a firing interval of 288° CA.

Deactivating the cylinders may be carried out in any suitable way,including one or more of disabling spark, disabling fuel injection, anddisabling airflow to the inactive cylinder. For example, at 220, sparkignition to the deactivated cylinder may be disabled. A cylinder may becut off through deactivation of the applied ignition and thereby toreliably avoid an unwanted firing, for example by residual gasesremaining in the cylinder.

Fuel injection to the cut-off cylinder may be deactivated at 222. Asdescribed with respect to FIG. 1, direct injection is provided forsupplying fuel to the cylinders. In principle the fuel supply of acutoff cylinder could be maintained and a cylinder cutoff could beundertaken solely by deactivation of the applied ignition. However, thiswould be extremely disadvantageous with regard to the fuel consumptionand the pollutant emissions and would be at odds with the objectivebeing pursued by the partial cutoff, namely of reducing the fuelconsumption and improving engine efficiency. The direct injection allowsa cut-off and selective cut-in of the fuel supply from one operatingcycle to the next. This also serves to prevent any fuel introduced beingaccidentally and spontaneously ignited due to the high temperatures ofthe residual combustion gases in the cylinder, even in the absence ofapplied ignition. In contrast to direct injection, it is not possiblewhen using inlet manifold injection to ensure that the delivery of fuelto a cutoff cylinder will be completely stopped, as the principle ofmanifold injection involves wetting the walls in the intake tract withfuel.

Additionally, the direct injection of the fuel into the cylinders, likethe partial cutoff itself, provides some dethrottling of the internalcombustion engine, so that the two measures, the partial cutoff on theone hand and the direct injection on the other, enhance one another inthe dethrottling.

With fuel injection disabled, the aspirated combustion air can stillflow through the cutoff cylinder, the absence of any fuel chargeensuring that there is no combustible or ignitable fuel-air mixtureavailable and that consequently—even if the ignition spark wereintroduced—no firing and no combustion occurs in this cylinder.

During the partial cutoff the cutoff cylinder basically makes nocontribution to the power output of the internal combustion engine. Ifthe fresh air feed is not cut off but is instead maintained, the air fedto the cutoff cylinder continues to play a part in the four workingstrokes—induction, compression, expansion and exhaust—so that not onlydoes the cutoff cylinder not deliver any power, but work for the chargecycle has to be invested in this cylinder, which impairs the efficiency,that is to say it is thermodynamically disadvantageous.

For this reason, the air feed to a cutoff cylinder may be stopped at224. Here the deactivated cylinder may be isolated from the combustionair supply by means of a shutoff valve. Where necessary the intake tractmay be modified, each cylinder being equipped with a separate intakeport, for example. Replacing the conventional intake system with amodified intake tract makes the concept suitable for retrofitting.

In some embodiments, in multi-cylinder internal combustion engines inwhich the cylinders are equipped with lift valves for charge cyclepurposes, the lift valves of a cutoff cylinder may be deactivated. Acutoff cylinder then functions with valves closed during the partialcutoff. In this case the air present in the cylinder during compressionis compressed by the piston moving upwards, the compressed air storingthe work or energy introduced like a spring, before delivering it again,that is to say introducing it into the crankshaft drive, in the nextstroke, the succeeding expansion stroke. Apart from a slight frictionpower deriving from the moving parts of the engine, no further lossesoccur, for which reason it is thermodynamically more advantageous todeactivate the valves of a cutoff cylinder than to allow a continuingflow of air through this cylinder during the charge cycle.

In some embodiments where airflow through the cut-off cylinder isdisabled, the cylinders may be supplied with fuel by means of intakemanifold injection, since in the cutoff state with valves closed and theintake manifold injection deactivated no fuel can get into the cylinderfrom the intake tract, in particular from the fuel-wetted walls.

At 226, the fuel amount delivered to the active cylinders and thethrottle position may be adjusted so that torque and the desiredair-fuel ratio within each cylinder are maintained. For example, whentransitioning from an operating mode where all cylinders are fired tothe partial cutoff mode, the throttle valve and fuel injection amountsmay be adjusted to maintain operator-requested torque. In advantageousembodiments of the multi-cylinder internal combustion engine anadjustable throttle valve is provided for load control. One advantage ofthe adjustable throttle valve is that on activation or deactivation ofthe partial cutoff, that is to say of one cylinder, the engine torquedoes not fall or rise and the driver does not have to adjust theaccelerator pedal in line with this in order to maintain the load, aswould be the case with a non-adjustable throttle valve.

The adjustable throttle valve is preferably an electronically controlledthrottle valve and an engine control assumes control of this throttlevalve. This embodiment is also preferable in terms of the costs.Embodiments in which the throttle valve is adjustable by a closed-loopmethod are advantageous here.

Thus, method 200 includes operating an engine having an odd number ncylinders. When engine speed and load are above a threshold, allcylinders may be fired by activating fuel delivery, spark ignition, andintake and exhaust valve actuation for each cylinder every crankshaftcycle. When engine speed and load are below the threshold, a subset ofthe cylinders may be fired by deactivating fuel delivery, sparkignition, and intake and exhaust valve actuation for one cylinder everycrankshaft cycle such that each cylinder is cut off once every ncrankshaft cycles. In doing so, throttling losses may be prevented, thusincreasing engine efficiency, and a balanced firing order may bemaintained.

The method of FIG. 2 also includes operating an engine having an oddnumber of cylinders. Operating the engine includes, at greater output,spark igniting directly injected fuel in all cylinders, with eachcylinder firing only once every two crankshaft rotations in a firstfiring order, and at lower output, spark igniting directly injected fuelin all cylinders, with each cylinder firing only once every fourcrankshaft rotations in a second, different firing order. The methodalso includes the first and second firing orders comprising cylinderfiring at evenly spaced intervals, the second firing order including aninterval between cylinder firings that is twice as long as an intervalbetween cylinders firings of the first firing order.

FIG. 3 shows a diagram 300 of the ignition points of the three cylinders1, 2, 3 of a three-cylinder internal combustion engine with appliedignition in standard operation whereby all cylinders are active. Instandard operation, in which all three cylinders 1, 2, 3 are fired, thethree cylinders 1, 2, 3 arranged in line are fired in succession in thefiring order 1-2-3 and at an interval of 240° CA (illustrated by zigzagarrows). A regular firing pattern prevails at a firing interval of 240°CA.

The four working strokes of the internal combustion engine encompass tworevolutions of the crankshaft and form one cycle. As can be seen fromFIG. 3, the first outer cylinder 1 is fired at 0° CA, the second innercylinder 2 at 240° CA and the third outer cylinder 3 at 480° CA. Thelast crank angle mark 720° CA represents the end of the first cycle andthe start of the second following cycle, so that the crank angle here iscounted from 0° CA again.

FIG. 4 shows a diagram 400 of the ignition points of the three cylinders1, 2, 3 of the three-cylinder internal combustion engine with appliedignition in partial cutoff. In partial load operation one cylinder 1, 2,3 is cut off in the context of a partial cutoff and only two cylinders1, 2, 3 are fired, the cylinders 1, 2, 3 being operated intermittentlyduring the partial cutoff and each cylinder 1, 2, 3 being fired once andcut off once within two cycles.

Each cylinder 1, 2, 3 is fired and cut off in turn, so that in partialload operation the cylinders 1, 2, 3 are fired in the firing order 1-3-2at an interval of 480° CA. During the partial cutoff, as also in normaloperation, a regular firing pattern prevails, the firing interval being480° CA.

As can be seen from FIG. 4, the first outer cylinder 1 is fired in thefirst cycle at 0° CA, the third outer cylinder 3 in the first cycle at480° CA and the second inner cylinder 2 in the second cycle at 240° CA.

FIG. 5 is a diagram 500 illustrating a transition from standard, fullcylinder firing operation to partial cutoff operation. Similar to FIGS.3 and 4, three cylinders are depicted with a starting firing order of1-2-3 at an interval of 240° CA. Additionally, the timing of each enginestroke, intake, compression, expansion, and exhaust, are depicted beloweach cylinder. At 0° CA, the first cylinder is at TDC of the compressionstroke and thus fires. A transition to the partial cutoff operationoccurs at 502, indicated by the dashed line, due to engine load droppingbelow a threshold, for example. However, because the transition occurstowards the end of the compression stroke for the second cylinder, fuelmay already have been injected to the second cylinder, and deactivatingthe second cylinder may result in wasted fuel and degraded emissions.Thus, the second cylinder is fired at 240° CA and cylinder cutoff beginsat the third cylinder, which is deactivated and therefore not fired at720° CA. In this way, even though partial cutoff operation was indicatedat 502 based on engine load, actual operation in the partial cutoff modewas delayed based on fuel economy and emissions. Transition to thepartial cutoff mode may be delayed by any suitable parameter, such ascatalyst temperature, engine speed, etc.

FIG. 6 is a diagram 600 illustrating a transition from operation inpartial cutoff to standard, full cylinder operation. At 602, atransition to the standard full cylinder operation is indicated, basedon engine load exceeding a threshold, for example. Cylinder two is firedprevious to the transition, and thus cylinder three is the next cylinderin the standard firing order. However, because the transition isinitiated late in the compression stroke of cylinder three, any fueldelivered may not have time to adequately mix prior to ignition,resulting in degraded emissions. As a result, cylinder three is skippedand full cylinder operation is resumed at cylinder one. In this way,even though standard operation was indicated at 602 based on engineload, actual operation in the standard mode was delayed based onemissions. Transition to the standard mode may be delayed by anysuitable parameter, such as catalyst temperature, engine speed, etc.

It will be appreciated that the configurations and methods disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1. A method, comprising operating a multi-cylinder direct-fuel-injectioninternal combustion engine with spark ignition, in which an odd number(n) of cylinders is arranged in line; and during partial-load operationwhen engine load is below threshold, adjusting engine airflow andenabling a partial cutoff of the cylinders, the partial cutoffcomprising operating each cylinder only intermittently such that eachcylinder is fired and cut off in turn at an interval of (2*720° CA)/n.2. The method as claimed in claim 1, wherein the engine isthree-cylinder, in-line engine, and further comprising: duringnon-partial load operation when engine load is above the threshold,operating the engine in standard operation whereby the three cylindersare fired in sequence in an ignition order of 1-2-3 at an interval of240° CA: and in partial-load operation when engine load is below thethreshold, operating the engine in a partial cutoff mode, wherein duringthe partial cutoff each cylinder is operated intermittently such thateach cylinder is fired and cut off in turn with a modified firing orderof 1-3-2 at a firing interval of 480° CA.
 3. The method as claimed inclaim 1, wherein the engine is a spark ignited, five-cylinder, in-lineengine, and further comprising: during non-partial load operation whenengine load is above the threshold, operating the five cylinders instandard operation whereby the cylinders are fired in sequence in anignition order of 1-2-4-5-3 at an interval of 144° CA; and duringpartial-load operation when engine load is below the threshold,operating the engine in a partial cutoff mode, wherein during thepartial cutoff each cylinder is operated intermittently such that eachcylinder is fired and cut off in turn with a modified firing order of1-4-3-2-5 at a firing interval of 288° CA.
 4. The method as claimed inclaim 1, wherein a fuel supply to a cutoff cylinder is deactivated. 5.The method as claimed in claim 1, wherein the engine includes an intakesystem for feeding air, and wherein air feed to a cutoff cylinder isstopped.
 6. The method as claimed in claim 1, wherein the cylinders areequipped with lift valves for charge cycle purposes, and wherein thelift valves of a cutoff cylinder are deactivated.
 7. The method asclaimed in claim 1, wherein the spark ignition of a cutoff cylinder isdeactivated.
 8. The method as claimed in claim 1, wherein the predefinedload, below which a partial cutoff ensues, varies as a function ofengine speed.
 9. A multi-cylinder internal combustion engine,comprising: an odd number n of cylinders (n≧3), arranged in line; anapplied ignition system; a fuel system for delivering fuel to thecylinders; an exhaust gas recirculation system; and a controller havingcomputer-readable instructions stored therein, the instructionsexecutable to: during partial-load operation when engine load is belowthreshold, enable a partial cutoff of the cylinders, the partial cutoffcomprising operating each cylinder intermittently such that eachcylinder is fired and cut off in turn at an interval of (2*720° CA)/n,wherein each cylinder is cut off through deactivation of the appliedignition.
 10. The multi-cylinder internal combustion engine as claimedin claim 9, wherein each cylinder is equipped with a spark plug forintroduction of the applied ignition.
 11. The multi-cylinder internalcombustion engine as claimed in claim 9, wherein each cylinder isequipped with an injection nozzle to supply fuel by means of directinjection.
 12. The multi-cylinder internal combustion engine as claimedin claim 9, wherein each cylinder is equipped with lift valves forcharge cycle purposes, and wherein an adjustable throttle valve isprovided for load control.
 13. A method, comprising: operating an enginehaving an odd number of cylinders; at greater output, spark ignitingdirectly injected fuel in all cylinders, with each cylinder firing onlyonce every two crankshaft rotations in a first firing order; and atlower output, spark igniting directly injected fuel in all cylinders,with each cylinder firing only once every four crankshaft rotations in asecond, different firing order by sequentially deactivating eachcylinder.
 14. The method of claim 13, wherein at lower output, eachcylinder is fired and deactivated.
 15. The method of claim 13, whereinat lower output each cylinder is cut off in turn, with only one cylinderat a time being cut off and remaining cylinders being in operation. 16.The method of claim 13, wherein the first and second firing orderscomprise cylinders being fired at evenly spaced intervals.
 17. Themethod of claim 16, wherein the second firing order includes an intervalbetween cylinder firings that is twice as long as an interval betweencylinders firings of the first firing order.
 18. The method of claim 13,wherein the engine comprises five cylinders and further comprising: atgreater output, firing a cylinder every 144° CA; and at lower output,firing a cylinder every 288° CA.
 19. The method of claim 13, wherein theengine comprises three cylinders and further comprising: at greateroutput, firing a cylinder every 240° CA; and at lower output, firing acylinder every 480° CA.
 20. The method of claim 13, further comprising,when transitioning from firing all cylinders to firing a subset of thecylinders, adjusting an adjustable throttle valve and a fuel amountdelivered to each active cylinder in order to maintain torque.